Coexistent channel access method

ABSTRACT

A method is presented for transmitting a data packet in a wireless local area network. A physical layer protocol data unit (PPDU) is generated, The PPDU indicates that the PPDU is to be transmitted to a plurality of receivers. The PPDU includes a legacy-short training field (L-STF), a legacy-long training field (LTF), a legacy-signal field (L-SIG), a signal field and a plurality of data streams. The PPDU is transmitted to the plurality of receivers through a plurality of subchannels. The signal field includes stream information and subchannel information. The stream information indicates at least one of the plurality of data streams assigned to each of the plurality of receivers. The subchannel information indicates at least one of the plurality of subchannels through which a corresponding data steam assigned to each of the plurality of receivers is transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 14/976,655 filed on Dec. 21, 2015, which is a Continuation ofU.S. patent application Ser. No. 14/454,602 filed on Aug. 7, 2014 (nowU.S. Pat. No. 9,240,874 issued on Jan. 19, 2016), which is aContinuation of U.S. patent application Ser. No. 13/202,028 filed onAug. 31, 2011 (now U.S. Pat. No. 8,830,973 issued on Sep. 9, 2014),which is filed as the National Phase of PCT/KR2009/006940 filed on Nov.24, 2009, which claims the benefit under 35 U.S.C. §119(e) to U.S.Provisional Application No. 61/153,299 filed on Feb. 18, 2009, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

BACKGROUND OF THE INVENTION

The present invention relates to a wireless communication system and,more particularly, to channel accessing and data stream transmissiontechnique in a wireless local area network (WLAN) system in which alegacy station exists.

Recently, diverse wireless communication technologies are underdevelopment in line with the advancement of information communicationtechnology. Among them, a wireless local area network (WLAN) is atechnique allowing users to wirelessly access the Internet by usingmobile terminals such as personal digital assistants (PDAs), lap topcomputers, portable multimedia players (PMPs), and the like, at homes,offices or in a particular service providing area based on a radiofrequency technology.

Since IEEE (Institute of Electrical and Electronics Engineers) 802, astandardization organization of a WLAN technique, was established inFebruary 1980, a great deal of standardization works have beenconducted.

The early WLAN technique supported the rate of 1˜2 Mbps throughfrequency hopping, spread spectrum, infrared communications, and thelike, by using a 2.4 GHz frequency based on IEEE 802.11, and recently, amaximum rate of 54 Mbps can be supported by applying orthogonalfrequency division multiplex (OFDM) technology to the WLAN. Further,IEEE 802.11 are putting standards of various techniques, such asimprovement of quality of service (QoS), allowing compatibility ofaccess point (AP) protocols, achievement of security enhancement,measurement radio resource measurement, wireless access vehicularenvironment, ensuring fast roaming, establishing a mesh network,interworking with an external network, wireless network management, andthe like, into practical use or are still developing them.

Among the IEEE 802.11, IEEE 802.11b supports a maximum of 11 Mbscommunication speed while using the frequency band of 2.4 GHz. IEEE802.11a, which has been commercialized following the IEEE 802.11b, usesthe frequency band of 5 GHz, not 2.4 GHz, to reduce the influence ofinterference compared with the considerably congested frequency band of2.4 GHz and has a communication speed increased up to a maximum 54 Mbpsby using the OFDM technique. However, IEEE 802.11a has shortcomings inthat its communication distance is shorter than that of IEEE 802.11b.Meanwhile, IEEE 802.11g uses the frequency band of 2.4 GHz, like IEEE802.11b, to implement a communication speed of a maximum 54 Mbps andsatisfies backward compatibility, and as such, IEEE 802.11g receivesmuch attention. Also, IEEE 802.11b is superior to IEEE 802.11a, in theaspect of the communication distance.

IEEE 802.11n has been lately stipulated as a technique standard toovercome the limitation in the communication speed which has beenadmitted as a weak spot of the WLAN. IEEE 802.11n aims to increase thespeed and reliability of a network and extend an operation distance of awireless network.

In more detail, IEEE 802.11n supports a high throughput (HT) of morethan a maximum 540 Mbps as a data processing speed, and is based on amultiple input and multiple output (MIMO) technique using multipleantennas at both ends of a transmission part and a reception part tominimize a transmission error and optimize a data rate.

Also, IEEE 802.11n standard may use orthogonal frequency divisionmultiplex (OFDM) to increase the speed as well as using a coding schemethat transmits several duplicates to enhance data reliability.

As the WLAN is widely spreading and applications using WLAN arediversified, recently, the necessity for a new WLAN system emerges tosupport a higher throughput than the data processing speed supported byIEEE 802.11n.

A very high throughput (VHT) WLAN system is one of the newly proposedIEEE 802.11 WLAN systems in order to support a data processing speed of10 Gbps or faster in a MAC service access point (SAP). The term of VHTWLAN system is arbitrary, and currently, a feasibility test is performedon a 4.times.4 MIMO (or 5.times.4 MIMO) and a system using a channelbandwidth of 80 MHz or higher to provide throughput of 1 Gbps or faster.

Aiming at satisfying an aggregated throughput of 1 Gbps, the VHT WLANsystem also has the purpose of achieving a minimum 500 Mbps forone-to-one communications between terminals (e.g., user equipments(UEs)). If an offered load of VHT stations is 500 Mbps, it would beeffective for the several VHT stations to simultaneously use channels tosatisfy the aggregated throughput of 1 Gbps of a VHT basic service set(BSS).

The case of the VHT WLAN system has been described, but in most caseswhere UEs in conformity with the standards of the WLAN system and legacyUEs coexist, the legacy UEs support a narrower channel bandwidth and asmaller number of antennas than those of the UEs supporting the currentstandard of the WLAN system. Thus, while the legacy UEs use channels,some channel bandwidths and antennas are not in use, resulting in awaste of radio resources.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to seek an effectiveuse of radio resources in transmitting a data stream in a wireless localarea network (WLAN) system in which legacy stations exist.

Another object of the present invention is to reduce a waste of radioresources or antennas in the case where an access point (AP) and astation supporting multiple antennas and a station that does not supportmultiple antennas coexist.

According to an aspect of present invention, a method for transmitting acoexistent data stream, the method including: transmitting coexistentdata stream transmission information including transmission powerinformation of a first data stream targeted for a first station andtransmission power information of a second data stream targeted for asecond station in an environment in which the first station, a legacystation, coexists with a second station, a station supporting a wirelesslocal area network (WLAN) system evolved further than the first station;and transmitting, by an access point (AP), the first and second datastreams to the second station and the first station, wherein the APtransmits the first data stream with a higher transmission power levelthan that of the second data stream according to the coexistent datastream transmission information.

According to another aspect of present invention, a method fortransmitting a coexistent data stream, the method including: when afirst data stream is targeted for a second station and a third datastream is targeted for a first station in an environment in which thefirst station, a legacy station, coexists with a second station, astation supporting a wireless local area network (WLAN) system evolvedfurther than the first station, generating, by an access point (AP), asecond data stream, an inverse stream of the first data stream; andtransmitting the first data stream, the second data stream, and thethird data stream to the first station and the second station, whereinan integrated stream of the first to third data streams is the same asthe third data stream.

According to still another aspect of present invention, a method fortransmitting a coexistent data stream, the method including:transmitting, by an access point (AP), coexistent data streamtransmission information to a first station, a legacy station, and asecond station supporting a wireless local area network (WLAN) systemevolved further than the first station; transmitting a first data streamto the first station via a first subchannel among an entire channelbandwidth according to the coexistent data stream transmissioninformation; and transmitting a second data stream to the second stationvia a subchannel, excluding the first subchannel, among the entirechannel bandwidth according to the coexistent data stream transmissioninformation.

According to still another aspect of present invention, a wirelesscommunication device including: a processor configured to generatecoexistent data stream transmission information including transmissionpower information of first data stream and the second data stream to betransmitted to first and second stations, and adjust the transmissionpower of first data stream and the second data stream according to thetransmission power information, in an environment in which the firststation, a legacy station coexists with a second station, a stationsupporting a wireless local area network (WLAN) system evolved furtherthan the first station; and a radio frequency (RF) unit configured totransmit the coexistent data stream transmission information andtransmit the first data stream and the second data stream with theadjusted transmission power.

According to still another aspect of present invention, a wirelesscommunication device including: a processor configured to generate asecond data stream, an inverse stream of a first data stream, when thefirst data stream is targeted for a second station and a third datastream is targeted for a first station in an environment in which thefirst station, a legacy station coexists with a second station, astation supporting a wireless local area network (WLAN) system evolvedfurther than the first station; and a radio frequency (RF) unitconfigured to transmit the first data stream, the second data stream,and the third data stream to the first and second stations, wherein anintegrated stream of the first to third data streams is the same as thethird data stream.

In an environment in which legacy stations coexist, a data stream can besimultaneously transmitted to every station. In addition, a waste ofradio resources that may be generated as data is transmitted to thelegacy stations in the coexistence environment. To this end, a method oftransmitting a control signal such that it can be recognized by stationsincluding the legacy stations in the coexistence environment andtransmitting the data stream by effectively using antennas and radioresources is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the configuration of a wireless local area network(WLAN) system to which an exemplary embodiment of the present inventioncan be applicable.

FIG. 2 illustrates a method for transmitting a coexistent data streamaccording to one exemplary embodiment of the present invention.

FIG. 3 illustrates a method for transmitting a coexistent data streamaccording to another exemplary embodiment of the present invention.

FIG. 4 illustrates data streams transmitted in an exemplary embodimentof the present invention described with reference to FIG. 3.

FIGS. 5 and 6 illustrate physical layer convergence procedure (PLCP)frame formats according to an exemplary embodiment of the presentinvention.

FIG. 7 is a schematic block diagram of a wireless communication devicefor performing the coexistent data stream transmission method accordingto an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates the configuration of a wireless local area network(WLAN) system to which an exemplary embodiment of the present inventioncan be applicable.

The WLAN system illustrated in FIG. 1 includes one or more basic servicesets (BSSs). A BSS refers to a set of stations (STAs) that cancommunicate with each other in synchronization, not a concept indicatinga particular area. Like the WLAN system to which the exemplaryembodiments of the present invention are applicable, a BSS that supportsthe data processing at a high speed of 1 GHz or faster at a MAC SAP iscalled a VHT BSS.

The VHT BSS can be classified into an infrastructure BSS and anindependent BSS (IBSS). FIG. 1 shows infrastructure BSSs.

The infrastructure BSSs (BSS1 and BSS2) include one or more of non-APSTA1, non-AP STA3, and non-AP STA4, access points (APs) (AP STA1 and APSTA2), stations providing a distribution service, and a distributionsystem (DS) connecting the plurality of APs (AP STA1 and AP STA2). Inthe infrastructure BSS, the AP stations manage the non-AP stations ofthe BSSs.

Meanwhile, the IBSS is a BSS operating in an ad-hoc mode. Because theIBSS does not include an AP VHT STA, it does not have a centralizedmanagement entity. Namely, in the IBSS, non-AP stations are managed in adistributed manner. In the IBSS, every station may be a mobile station,and the IBSS establishes a self-contained network, not allowing anaccess to a distribution system (DS).

A station (STA) is an arbitrary functional medium including a mediumaccess control (MAC) and wireless-medium physical layer (PHY) interfaceconforming to the institute of electrical and electronics engineers(IEEE) 802.11 standard. In a broad sense, the STAs include both AP andnon-AP STAs. In a multi-channel environment (to be described), a stationsupporting data processing at a very high speed of 1 GHz or higher iscalled a VHT STA. The VHT WLAN system to which the exemplary embodimentsof the present invention is applicable, stations included in the BSSsinclude a VHT STA, a legacy station (e.g., a non-VHT station such as HTSTA and the like in conformity with IEEE 802.11n. That is, the stationscoexist in the environment.

Among STAs, mobile terminals manipulated by a user are the non-AP STAs(STA1, STA3, and STA4). Simply referring to a station may indicate anon-AP STA. In particular, a station without an indication as legacystation may refer to a station supporting the standard of the currentwireless communication system. Thus, in the VHT WLAN system, a stationgenerally indicates a VHT station and a non-VHT station is a legacystation.

The non-AP STA may be referred to by other names such as terminal,wireless transmit/receive unit (WTRU), user equipment (UE), mobilestation (MS), mobile terminal, mobile subscriber unit, or the like. Anon-AP STA supporting data processing at a high speed of 1 GHz or fasterin the multi-channel environment (to be described) may be also called anon-AP VHT STA or simply a VHT STA.

The APs (AP1 and AP2) are functional entities for providing an access tothe DS by way of a wireless medium for an STA associated thereto. In theinfrastructure BSS including the APs, in principle, communicationsbetween non-AP STAs are made by way of the APs, but when a direct linkhas been established, the non-AP STAs can directly communicate with eachother.

The AP may be also called by other names such as centralized controller,base station (BS), node-B, base transceiver system (BTS), sitecontroller, and the like, than the AP. In the multi-channel environment(to be described), an AP supporting high speed data processing at 1 GHzor faster is called a VHT AP.

A plurality of infrastructure BSSs may be connected via the DS. Theplurality of BS Ss connected via the DS is called an extended serviceset (ESS). STAs included in the ESS may communicate with each other, andthe non-AP STA may move from one BSS to another BSS within the same ESSwhile seamlessly performing communication.

The DS is a mechanism allowing one AP to communicate with another AP.Through the DS, an AP may transmit a frame for STAs associated to theBSS managed by the AP, transfer a frame when one STA moves to anotherBSS, or transmit or receive frames to and from an external network suchas a wireline network. The DS is not necessarily a network. Namely, theDS is not limited to any form so long as it can provide a certaindistribution service defined in the IEEE 802.11 standard. For example,the DS may be a wireless network such as a mesh network or a physicalstructure connecting the APs.

In the case of assuming the VHT WLAN system, here, the AP supports theVHT system unless there is a limitation that the AP is a legacy AP. Inthe VHT BSS, a legacy station supporting and a station supporting theVHT system coexist.

In the VHT WLAN system, the non-VHT station, a legacy station, is, forexample, an STA supporting a system following IEEE 802.11a/b/gstandards. In case of the IEEE 802.11a/b/g STA, it supports only asingle antenna, so it cannot support MIMO. Thus, in the VHT system, theAP have no choice but to transmit only a single stream to the IEEE802.11a/b/g STA.

In addition, the IEEE 802.11a/b/g STA supports a channel bandwidth of 20MHz, failing to support a wider channel bandwidth (e.g., channelbandwidth of 40 MHz or 80 MHz). Thus, although the VHT AP is able tosupport the channel bandwidth of 80 MHz, it is allowed to use only thechannel bandwidth of 20 MHz when transmitting data to the IEEE802.11a/b/g.

In the VHT WLAN system, if the AP supports five antennas and a legacystation (e.g., a station following the an IEEE 802.11a/b/g/n standard)supports one antenna, when the AP transmits data to the legacy station,only one of the five antennas is used while the other remaining fourantennas are not in use.

If the AP supports a channel bandwidth of 80 MHz and the legacy stationsupports only a channel bandwidth of 20 MHz, when the AP transmits datato the legacy station, merely 20 MHz in the channel bandwidth of 80 MHzis used while the other remaining 60 MHz is not used.

The present invention proposes a scheme of allocating the otherremaining resources, which are not in use while the AP transmits data tothe legacy station, to other stations. In the following description, aVHT system having the 4.times.4 MIMO (or 5.times.4 MIMO) and 80 MHzchannel bandwidth will be taken as an example.

Namely, the present invention relates to a channel accessing method orthe use of channels in data transmission in an environment in which thestation according to the current wireless communication system and thelegacy station coexist, which may be simply called a coexistent channelaccess mechanism. Here, the AP supporting the VHT WLAN system may havefour or more antennas and a channel bandwidth of 80 MHz or wider.

FIG. 2 illustrates a method for transmitting a coexistent data streamaccording to one exemplary embodiment of the present invention.

As stated above, the present invention proposes a method and system fortransmitting common control information in a communication system inwhich a legacy station and a station according to the communicationsystem which has evolved from the legacy communication system coexist.

In the following description, the legacy station will be referred to asa first station, and the station according to the evolved communicationsystem will be referred to as a second station. The first station may bea station following a standard before 802.11n, while the second stationmay be a station following a standard after 802.11n. The secondcommunication system may be a VHT WLAN system.

As afore-mentioned, in the WLAN environment according to an exemplaryembodiment of the present invention, the first and second stationscoexist in the WLAN system. For example, the VHT station and the non-VHTstation coexist in the VHT WLAN system. The first station supports asingle antenna and the second station supports multiple antennas. Also,it is assumed that the second station supports a wider channel bandwidththan that of the first station.

Because the first station does not support multiple antennas, while theAP is transmitting data to the legacy station, the first station cannotuse antennas or a channel bandwidth which could be used if the APtransmits a data stream to the second station. Thus, resources arewasted.

In the antenna coexistence scheme, the AP allocates antennas separatelyto the first and second stations, and simultaneously transmits datastreams separately to the first and second stations. In this case,transmission power of each data stream is adjusted to be different(S210).

Before transmitting the data streams, the AP may transmit coexistentdata stream transmission information to the first and second stations.The coexistent data stream transmission information may includetransmission power information. The first station receives only a datastream with the most powerful signal strength via the single antenna,while the second station can receive every data stream by each differentantenna. Thus, the second station needs prior information regardingtransmission power with which each data stream is to be transmitted.Namely, in the present exemplary embodiment, the coexistent data streamtransmission information may be information particularly required by thesecond station.

In the present exemplary embodiment, the coexistent data streamtransmission information is information about transmission power of eachdata stream. However, in a different embodiment, the coexistent datastream transmission information may include information about throughwhich subchannel each stream is to be transmitted, information about achannel bandwidth used for transmitting each stream, information aboutwhether or not there is a redundant stream among the streams, and thelike.

The AP increases transmission power of a data stream to be transmittedto the first station and decreases transmission power of a data streamto be transmitted to the second station, and transmits the data streams(S220). As a result, at the position of a reception side, the signalstrength of the data stream targeted for the first station is recognizedto be the most powerful, while that of the data stream targeted for thesecond station is recognized to be relatively weak.

Thus, the data stream transmitted to be targeted for the second stationacts as interference to the first station. Namely, the first stationreceives only the single data stream whose signal strength is recognizedto be most powerful as its transmission power strong among the pluralityof data streams which have been transmitted with transmission power setto be different from the AP. This is like the case of a capture effect.

In this case, a modulation coding scheme (MCS) value of the data streamtransmitted to be targeted for the first station must be determined inconsideration of the interference of the data stream transmitted to thesecond station.

The MCS value of the data stream targeted for the first station must beset to satisfy a minimum receiver sensitivity in determiningtransmission power of the data stream destined for the second station.When transmission power of each stream is differentiated, the AP needsto inform the second station about transmission power of each datastream in advance. To this end, a physical layer convergence procedure(PLCP) frame format may include a transmission power indicator withrespect to each data stream. Namely, in the coexistent data streamtransmission information, the transmission power information or thetransmission power indicator may be included in the PLCP frame formatand transmitted.

FIG. 3 illustrates a method for transmitting a coexistent data streamaccording to another exemplary embodiment of the present invention, andFIG. 4 illustrates data streams transmitted in an exemplary embodimentof the present invention described with reference to FIG. 3.

In an exemplary embodiment described with reference to FIG. 3, a firststation refers to a legacy station (e.g., a non-VHT STA in the VHTsystem), and a second station refers to a station (e.g., a VHT stationin a VHT WLAN system( ) supporting the standard of the evolved WLANsystem.

A method of transmitting inverse streams with respect to some of datastreams together in transmitting the data streams to the first andsecond stations will be described with reference to FIG. 3. In thepresent exemplary embodiment described with reference to FIG. 3,transmission power of the streams transmitted by the AP does not need tobe set to be different. Here, the some data streams transmitted togetherwith the inverse streams are data streams transmitted to be targeted forthe second station.

The AP transmits the data streams and inverse streams of the datastreams redundantly to the second station, so that the two data streamsare canceled out in their sum. As a result, the sum of the data streamstransmitted to the first station and the data streams and the inversestreams transmitted to the second station is equal to the data streamstransmitted to the first station. At the position of the first station,it receives the integrated stream 460 of the three types of datastreams, resulting in that the first station can normally receive thedata stream targeted for the first station.

To this end, the transmitter side may need to perform a process ofcorrecting the phases and amplitudes of the data streams such that thephases and the amplitudes of the respective data streams are shown to bethe same at the position of the receiver side, namely, at the positionof the first station. By correcting the phases and amplitudes, the datastreams in the mutually inverse stream relationship may be canceled out.Namely, the first and second data streams can be canceled out, and thethird and fourth streams may be canceled out.

The process of correcting the phases and/or amplitudes is performedthrough a channel estimation between the first and second stations, thereceivers, and the AP, the transmitter. In the exemplary embodiment inwhich the PLCP frame uses the inverse streams, the channel estimation isadvantageous in that its performance is determined regardless of an SINRof the first and second stations.

With reference to FIG. 4, in the VHT system according to an exemplaryembodiment of the present invention, the AP supports five antennas andmay transmit five data streams via the five antennas. The five datastreams may indicate a first data stream 410, a second data stream 420,a third data stream 430, a fourth data stream 440, and a fifth datastream 450.

In this case, the first data stream of the AP corresponds to datatargeted for the second station. The second data stream corresponds toan inverse stream with respect to the first data stream. The third datastream corresponds to another data targeted for the second station. Thefourth data stream is an inverse frame with respect to the third datastream. Here, the third data stream may be targeted for a terminal thatcan support the same wireless communication system as that of the secondstation. Finally, the fifth data stream corresponds to data targeted forthe first station, the legacy station.

First, the AP generates the first data stream 410, the second datastream 420 which is the inverse stream of the third data stream 430, andthe fourth data stream 440 (S310). And then, the AP transmits theintegrated stream 460 obtained by adding the original data streams andtheir inverse streams desired to be transmitted to the stations, to thefirst and second stations (S320). In this case, the AP may transmit theintegrated stream 460 in a broadcasting or unicasting manner.

The integrated stream 460 represents a stream obtained by integratingall of the first data stream 410, the second data stream 420, the thirddata stream 430, the fourth data stream 440, and the fifth data stream450, and the first station receives the integrated stream 460.

Here, as shown in FIG. 4, the first data stream 410 and the second datastream 420 are in the relationship that they are mutually inversestreams. Thus, when the first data stream 410 and the second data stream420 are added to be transmitted, they may be seen to be canceled out.Likewise, the third data stream 430 and the fourth data stream 440 arealso in the relationship that they are mutually inverse streams, so whenan integrated stream is generated, the third and fourth data streams 430and 440 are canceled out. Consequently, the phase of the integratedstream 460 of the first to fifth data streams 410 to 450 is the same asthat of the fifth data stream 450.

In order to allow the first and second data streams and the third andfourth data streams to be completely canceled out, the AP may correctthe phases and amplitudes of the second and fourth data streams.

Accordingly, the first station can receive the fifth data stream 450 byreceiving the integrated stream 460. Meanwhile, the second station mayseparately recover the first to fifth data streams 410 to 450 from theintegrated stream.

That is, although the second station receives the integrated stream, itcan separately restore the first data stream 410 or the third datastream 430. However, the first station may not be able to separatelyrestore the data stream due to the limitation in the number of supportedantennas or the channel bandwidth.

Here, the second and fourth data streams 420 and 440, the inversestreams, correspond to redundant data, and the VHT stations can purelyreceive the first and third data streams. In addition, the second andfourth data streams 420 and 440, the inverse streams, may be used torecover a signal when the first and third data streams 410 and 430 havean error.

Here, the coexistent data stream transmission information may beprovided to the station before transmission of the data streams. Thecoexistent data stream transmission information according to the presentexemplary embodiment described with reference to FIGS. 3 and 4 includeswhether or not each data stream is an inverse stream or to which datastream, an inverse stream corresponds, and the like.

FIGS. 5 and 6 illustrate PLCP frame formats according to an exemplaryembodiment of the present invention. The frame formats illustrated inFIGS. 5 and 6 shows VHT PLCP frame formats that can provide informationregarding the use of channels to stations in a situation in which astation and a legacy station coexist. Also, in the present exemplaryembodiment, the legacy station will be referred to as a first station,and a station following the evolved communication system will bereferred to as a second station.

The PLCP frame formats in conformity with the IEEE 802.11n standard willnow be described. The PLCP frame formats include three modes of frameformats: non-HT format, HT mixed format, and Greenfield format. In thepresent exemplary embodiment, the PLCP frame formats of the VHT mixedformat and the Greenfield format, among the three modes of non-VHTformat, the VHT mixed format, and the Greenfield format, will bedescribed by taking a VHT, not HT, WLAN system as an example.

The non-VHT format is a structure for compatibility between the legacystation and the VHT station. The VHT mixed format illustrated in FIG. 5is the same as the non-VHT from L-STF to L-SIG, and uses the followingVHT-SIG signal. Thus, it is noted that the FHT station has the mixedformat. The Greenfield format illustrated in FIG. 6 is a non-compatibleformat which can be received only by the VHT station.

The PCLP frame format includes a PLCP preamble, a PCLP header, and data.The PLCP preamble is a signal for synchronization of an OFDM physicallayer and channel estimation. The PLCP preamble includes a shorttraining field (STF) and a long training field (LTF).

The STF performs functions of signal detection, automatic gain control(AGC), diversity selection, fine time synchronization, and the like, andthe LTF performs functions of channel estimation, a fractionalmultiplication frequency error estimation, and the like.

Of them, the L-STF, an STF for the legacy station, is used for AGC,timing synchronization, and rough frequency synchronization. An L-LTF,an LTF for the legacy station, is used for fine frequency offsetestimation and channel estimation of the legacy station.

The L-SIG includes information about a data transmission rate and a datalength. By putting a value corresponding to the length of an actualframe into the length field, even the L-SIG can be decoded when802.11a/g terminals receive the mixed format frame.

The VHT-STF preamble is used for improvement of performance of AGC orfine AGC in the mixed format. In the Greenfield format, it is used forAGC, timing synchronization, and rough frequency synchronization.

A VHT-LTF may be used for MIMO channel estimation. Because channels asmany as time and space streams should be estimated, the number ofHT-LTFs increases depending on the number of time and space streams.

A VHT-SIG transfers information about a VHT packet, when the VHT packetis transmitted. The VHT-SIG will be described in detail later.

FIG. 5 illustrates the PLCT frame format in case where the APsimultaneously transmits data streams to the second and first stationsin the environment in which the first and second stations coexist, andFIG. 6 illustrates the PLCP frame format in case where the AP transmitsdata streams to the second and first stations but not simultaneously.The PLCP frame format of FIG. 5 is indicated as VHT-mixed format PLCPprotocol data unit (PPDU), while the PLCP frame format of FIG. 6 isindicated as a VHT-greenfield format PPDU. This is because the VHT WLANsystem is illustrated as the WLAN system, and the types and standards ofthe WLAN systems do not limit the scope of the present invention.

The PLCP frame format illustrated in FIG. 5 and the PLCP frame formatillustrated in FIG. 6 are different according to whether or not theL-STF (Legacy-Short Training Field), L-LTF (Legacy-Long Training Field),L-SIG (Legacy-Signal) 510 for the first station, the legacy station, areincluded at a front portion of the header, and the other portions arethe same. The L-STF, L-LTF, and L-SIG 510 are fields for channelestimation of legacy stations. Channel estimation is made between thefirst station and the AP via the L-STF, L-LTF, and L-SIG 510. Thesefields indicate that a channel is busy, and are required to reset anetwork allocation vector (NAV). In addition, the VHT-STF and theVHT-LTF 530 and 610 are fields for channel estimation between the VHTstation and the AP.

When the AP transmits a data stream toward the legacy station (e.g., theabove-mentioned non-VHT station), it uses only a partial channel amongthe entire channel bandwidth. In an exemplary embodiment of the presentinvention, it is intended that the AP transmits data streams targetedfor the second station through a channel bandwidth which is not usedwhen the AP transmits a data stream toward the first station, the legacystation.

This method may be called a frequency division multiplex access scheme,and when this method is employed, the VHT PLCP frame format may includea channel bandwidth offset value with respect to each data stream.

In order to perform a coexistent channel access mechanism with thelegacy station, a PLCP frame format that can be recognized by both thefirst station, the legacy station, and the second station should beused. In addition, for a MIMO operation and an SDMA operation of secondstations, a currently supported WLAN system-specific PLCP frame formatneeds to be used.

To this end, the PLCP frame format proposed in the present invention mayfurther include the values of L-STF (Legacy Short Training Field), L-LTF(Legacy Long Training Field), and L-SIG (Legacy Signal) (540) for thelegacy station at the end portion of the PLCP header, namely,immediately before data 550 transmission.

In addition, in order to support the MIMO and SDMA operations of the VHTSTA, a channel estimation process through the VHT specific fields shouldbe performed, and in this case, the VHT specific fields are added infront of the L-STF, L-LTF, and L-SIG (540) in the header of the PLCPframe. Namely, the values VHT-STF, VHT-LTF (520, 620), and VHT-SIG (520,620) are transmitted before transmission of the L-STF, L-LTF, and L-SIG(540, 640).

The L-STF, L-LTF, and L-SIG (540, 640) finally transmitted in the PLCPheader are used only in the coexistent channel access mechanismaccording to the exemplary embodiment of the present invention. In caseof not simultaneously transmitting to the VHT station and the legacystation, the values L-STF, L-LTF, L-SIG (540, 640) do not need to beadded to the PLCP header immediately before transmission of the data(550 and 650).

In the coexistent channel accessing process, the AP may includeinformation about a transmission type of data streams, the use ofchannels, or the like, namely, the afore-mentioned coexistent datastream transmission information, in the VHT-SIG (520, 620) of the PLCPheader and transmit the same to the stations. For example, the VHT-SIG(520, 620) may include a value indicating the presence or absence of theL-STF, L-LTF, and L-SIG (540, 640). Namely, whether or not a pluralityof transmitted data streams are to be simultaneously transmitted to theVHT station and the legacy station may be indicated by indicatingwhether or not the L-STF, L-LTF, and L-SIG (540, 640) are subsequent tothe VHT-SIG.

For another example, the VHT-SIG (520, 620) may include an indicatorindicating a power level of transmission power corresponding to eachdata stream. Besides the transmission power indicator, the VHT-SIG (520,620) may include information about a channel bandwidth and a channelbandwidth offset with respect to each data stream. Namely, informationabout how much channel bandwidth is used to transmit each data stream orinformation about through which subchannel each data stream istransmitted may be included in the VHT-SIG (520, 620).

Also, the VHT-SIG (520, 620) may include information about which stationeach data stream is transmitted to be targeted for or information abouta destination of each data stream. Namely, whether or not acorresponding data stream should be transmitted to the second station orto the first station, the legacy station, is indicated in the VHG-SIG(520, 620).

Also, as mentioned above, the VHT-SIG (520, 620) may include informationallowing identifying to which data stream each data stream correspondsto as an inverse stream.

FIG. 7 is a schematic block diagram of a wireless communication devicefor performing the coexistent data stream transmission method accordingto an exemplary embodiment of the present invention.

The wireless communication device may be an AP of a WLAN system or astation of a wireless mesh network. The wireless communication deviceincludes a processor 710 and a radio frequency (RF) unit 720. A memory730 is connected to the processor 710 and stores various information fordriving the processor 710. The memory 730 may include a read-only memory(ROM), a random access memory (RAM), a flash memory, a memory card, astorage medium and/or any other storage units. Besides, the wirelesscommunication device may further include a display unit or a userinterface. Those elements are not illustrated in the drawing and itsdetailed description will be also omitted.

The processor 710 may include an application-specific integrated circuit(ASIC), a chip set, a logical circuit, and/or a data processing unit.The processor 710 may generate data or a control signal to betransmitted to other stations. The other stations include the firststation, the legacy station, the second station, the station supportingthe WLAN system more evolved than the first station, and the like. Acontrol signal to be transmitted to the first station and/or secondstation may be, for example, the coexistent data stream transmissioninformation as described above. In case of transmitting data streamswith each different transmission power to the first and second stations,the coexistent data stream transmission information may be transmissionpower information of each data stream.

Here, a data stream targeted for the first station will be referred toas a first data stream, and a data stream targeted for the secondstation will be referred to as a second data stream. In this case, theprocessor 710 may adjust the transmission power of the first and seconddata streams such that it is different. In an exemplary embodiment ofthe present invention, the transmission power of the first data streamis set to be higher than that of the second data stream.

Instead of adjusting the transmission power, the processor 710 maygenerate inverse streams of the data streams and transmit them together.To this end, the processor 710 may generate coexistent data streamtransmission information in order to inform receiver side stations thatthe inverse streams are also transmitted together and/or which streamsare inverse streams.

The RF unit 720, connected to the processor 710, transmits radio signalsgenerated from the processor 710, or receives a radio signal transmittedby a different wireless communication device. The RF unit 720 mayinclude a baseband circuit for processing radio signals. The signaltransmission may be performed in a broadcasting manner or unicastingmanner. The wireless communication device performing the coexistent datastream transmission method according to an exemplary embodiment of thepresent invention supports multiple antennas. First, the RF unit 720 maytransmit the coexistent data stream transmission information.

Also, the RF unit 720 may transmit a plurality of data streams to eachstation via the multiple antennas. When the RF unit 720 transmits theplurality of data streams each with a different transmission powerlevel, if the receiver side station supports only a single antenna, thereceiver side station may receive only a data stream received with themost powerful signal strength and recognize the other data streams asinterference.

When the processor 710 generates inverse streams and transmits themtogether, the RF unit 720 may transmit the data streams and theirinverse streams via the multiple antennas. In this case, inverse streamsof only the data streams targeted for the second station supporting themultiple antennas or the relatively wider channel bandwidth may begenerated and transmitted. Then, resultantly, the first stationsupporting the single antenna or the relatively narrower channelbandwidth receives the integrated stream in which the data streamstargeted for the second station have been canceled out, thus receivingonly the data stream pertinent to the first station. The second stationsmay separately restore each data stream according to the coexistent datastream transmission information to normally receive only the data streampertinent to the second station.

The methods described so far may be implemented by processors such asmicroprocessors, controllers, microcontrollers, application specificintegrated circuits (ASICs), and the like, according to software orprogram codes coded to perform the methods, or the process of thestation illustrated in FIG. 3. Designing, developing, and implementingof the codes may be obvious to the skilled person in the art based onthe description of the present invention.

The preferred embodiments of the present invention have been describedwith reference to the accompanying drawings, and it will be apparent tothose skilled in the art that various modifications and variations canbe made in the present invention without departing from the scope of theinvention. Thus, it is intended that any future modifications of theembodiments of the present invention will come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a data packet in a wireless local area network, the method comprising: generating a physical layer protocol data unit (PPDU) indicating that the PPDU is to be transmitted to a plurality of receivers, wherein the PPDU includes a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal field (L-SIG), a first signal field, a second signal field and a plurality of data streams; and transmitting the PPDU to the plurality of receivers through a plurality of subchannels, wherein the first signal field includes bandwidth information indicating an entire bandwidth for all of the plurality of subchannels, and wherein the second signal field includes stream information and subchannel information, and the subchannel information indicates at least one of the plurality of subchannels through which a corresponding data stream assigned to each of the plurality of receivers is transmitted, and the stream information indicates at least one of the plurality of data streams in at least one subchannel assigned to each of the plurality of receivers.
 2. The method of claim 1, wherein the first and second signal fields further include identification information identifying the plurality of receivers.
 3. The method of claim 1, wherein a bandwidth for the plurality of subchannels is one of 20 MHz, 40 MHz and 80 MHz.
 4. The method of claim 1, wherein the L-STF is used for the plurality of receivers to estimate an automatic gain control and a coarse frequency offset and the L-LTF is used for the plurality of receivers to estimate a fine frequency offset.
 5. The method of claim 1, wherein the PPDU further includes an STF and an LTF, the STF is used for improving automatic gain control estimation in a multiple input multiple output (MIMO) transmission, and the LTF is used for estimating a MIMO channel based on the plurality of data streams.
 6. A device configured to transmit a data packet in a wireless local area network, the device comprising: a processor; and a memory operatively coupled with the processor and storing instructions that, when executed by the processor, causes the device to: generate a physical layer protocol data unit (PPDU) indicating that the PPDU is to be transmitted to a plurality of receivers, wherein the PPDU includes a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal field (L-SIG), a first signal field, a second signal field and a plurality of data streams, and transmit the PPDU to the plurality of receivers through a plurality of subchannels, wherein the first signal field includes bandwidth information indicating an entire bandwidth for all of the plurality of subchannels, and wherein the second signal field includes stream information and subchannel information, the subchannel information indicates at least one of the plurality of subchannels through which a corresponding data stream assigned to each of the plurality of receivers is transmitted, and the stream information indicates at least one of the plurality of data streams in at least one subchannel assigned to each of the plurality of receivers.
 7. The device of claim 6, wherein the first and second signal fields further include identification information identifying the plurality of receivers.
 8. The device of claim 6, wherein a bandwidth for the plurality of subchannels is one of 20 MHz, 40 MHz and 80 MHz.
 9. The device of claim 6, Wherein the L-STF is used for the plurality of receivers to estimate an automatic gain control and a coarse frequency offset and the L-LTF is used for the plurality of receivers to estimate a fine frequency offset.
 10. The device of claim 6, Wherein the PPDU further includes an STF and an LTF, the STF is used for improving automatic gain control estimation in a multiple input multiple output (MIMO) transmission, and the LTF is used for estimating a MIMO channel based on the plurality of data streams. 